Field of the Invention
The present invention relates to a surface or liner material for absorptive products such as paper diapers or sanitary napkins.
Statement of the Prior Art
Absorptive products now enjoying wide use such as disposable diapers, are composed of three layers arranged in the order of a surface or liner layer, an absorbent layer and a backing layer unpervious to liquid, from the layer contacting the skin of the user's body. The linear layer is required to have, in addition to strength and softness, fluid permeability that permits fluid excrement to be absorbed to reach rapidly the absorbent layer, and a dry touch nature that prevents the fluid excrement absorbed from flowing-back to the skin and presents a dry feel to the skin. To meet such requirements, nonwoven fabrics comprising hydrophobic fibers have frequently been used, as proposed in the following three U.S. patent specifications. U.S. Pat. No. 3,695,269 discloses absorbent products comprising at least two fibrous layers; one layer comprising a highly absorbent fibrous mass having excellent absorption and retention capacity for body fluids and exudates; and a second layer comprising a relatively dry, non-adherent, non-woven fabric facing made of relatively non-absorbent, hydrophobic, synthetic fibres bonded with a hydrophobic binder material and processed so as to be provided with increased loft and bulk properties. U.S. Pat. No. 4,041,951 teaches that a topsheet of the absorptive device, such as disposable diapers, presenting a dry feel to the user is preferably constructed from a moisture-pervious, generally hydrophobic, nonwoven fibrous web. U.S. Pat. No. 4,391,869 states that fibers suitable for use in the invention are resilient, synthetic, staple fibers which generally are hydrophobic. However, use of nonwoven fabrics having such strong hydrophobic nature has resulted in improvements in the dry touch nature, but led to a lowering in fluid permeability. To make use of both dry touch nature and fluid permeability in a well-balanced state, attempts have therefore been made to apply a finish comprising usual surfactants on the surface of hydrophobic fibers.
In recent years, diverse requirements have been imposed upon absorptive products. For absorptive products designed to be used at night in particular, it is required to retain suitable degrees of fluid permeability and dry touch nature ever after a repeated excretion and absorption of fluid excrement several times. In view of such a requirement, the liner materials formed of nonwoven fabrics comprising hydrophobic fibers having a conventional surface active agent deposited thereon have the disadvantage that, upon absorbing fluid excrement once or twice, that agent flows away, thus resulting in a sharp drop in fluid permeability.